System and method for safely flying unmanned aerial vehicles in civilian airspace

ABSTRACT

A system and method for safely flying an unmanned aerial vehicle (UAV), unmanned combat aerial vehicle (UCAV), or remotely piloted vehicle (RPV) in civilian airspace uses a remotely located pilot to control the aircraft using a synthetic vision system during at least selected phases of the flight such as during take-offs and landings.

CROSS REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/745,111 filed on Apr. 19, 2006.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates to the field of remotely piloted vehicles (RPVs)and unmanned aerial vehicles (UAVs). RPV is an older term for UAV. UCAVshall mean “Unmanned Combat Aerial Vehicle.” UCAV is also sometimesdefined as an “Uninhabited Combat Aerial Vehicle.” UCAV is a UAV that isintended for use in combat. UAS means “Unmanned Aerial System.” UCASmeans “Unmanned Combat Air System.” ROA means “Remotely OperatedAircraft.” The characteristics all these vehicles have in common is thatthere is no human pilot onboard and although they may be operatedautonomously they can also be controlled by a remotely located operatoror pilot. The term UAV shall be used as a generic term for suchvehicles. “Synthetic Vision” is the current term for three dimensionalprojected image data presented to the pilot or other observer. Anotherterm for “Synthetic Vision” is “Synthetic Environment.” An older termfor “Synthetic Vision” is “Virtual Reality.” The term “AugmentedReality” (AR) refers to a human/computer interaction in which synthetic,computer generated elements are mixed or juxtaposed with real worldelements in such a way that the synthetic elements appear to be part ofthe real world. A common method used by Augmented Reality systems is tocombine and overlay a synthetic vision system with the video from one ormore video or infrared cameras. Augmented Reality is also sometimesreferred to as “Enhanced Vision.” The term “Remote Pilot” shall mean thesame as “Remote Operator.” The term “Sense and Avoid” shall mean thesame as “See and Avoid.”

2. Prior Art

The use of Synthetic Vision in flying a UAV is taught by U.S. Pat. No.5,904,724 Method and apparatus for remotely piloting an aircraft issuedMay 18, 1999 to Margolin (the present Applicant) which is herebyincorporated by reference. From the Abstract:

-   -   A method and apparatus that allows a remote aircraft to be        controlled by a remotely located pilot who is presented with a        synthesized three-dimensional projected view representing the        environment around the remote aircraft. According to one aspect        of the invention, a remote aircraft transmits its        three-dimensional position and orientation to a remote pilot        station. The remote pilot station applies this information to a        digital database containing a three dimensional description of        the environment around the remote aircraft to present the remote        pilot with a three dimensional projected view of this        environment. The remote pilot reacts to this view and interacts        with the pilot controls, whose signals are transmitted back to        the remote aircraft. In addition, the system compensates for the        communications delay between the remote aircraft and the remote        pilot station by controlling the sensitivity of the pilot        controls.

The system by which an aircraft periodically transmits itsidentification, location, altitude, and bearing was taught by U.S. Pat.No. 5,153,836 issued Oct. 10, 1992 to Fraughton et al. and wasmaterially adopted by the FAA as Automatic DependentSurveillance-Broadcast (ADS-B). According the article Gulf of MexicoHelo Ops Ready for ADS-B in Aviation Week & Space Technology (Feb. 26,2007, page 56):

-   -   By the end of 2010, FAA expects to have the ADS-B system tested        and operationally acceptable for the NAS, with Houston Center        providing services in the Gulf region. By 2013, all of the U.S.        is scheduled to be covered with ground infrastructure.

Current Practice

The current practice in flying UAVs in civilian airspace is typified bythe report Sensing Requirements for Unmanned Air Vehicles by AFRL's AirVehicles Directorate, Control Sciences Division, Systems DevelopmentBranch, Wright-Patterson AFB OH, June 2004, which relies oncomputer-intelligence to use sensors to sense and avoid other aircraft.

According to the presentation entitled Developing Sense & AvoidRequirements for Meeting an Equivalent Level of Safety given by RussWolfe, Technology IPT Lead, Access 5 Project at UVS Tech 2006 this hadnot changed as of Jan. 18, 2006. Access 5 was a national projectsponsored by NASA and Industry with participation by the FAA and DOD tointroduce high altitude long endurance (HALE) remotely operated aircraft(ROA) to routine flights in the National Airspace System (NAS). Access 5started in May 2004 but when NASA withdrew its support (and funding) theIndustry members decided not to spend their own money and Access 5 wasdissolved at the end of 2005.

The presentation Integration into the National Airspace System (NAS)given by John Timmerman of the FAA's Air Traffic Organization (Jul. 12,2005) essentially says that under current UAS Operations in the NAS UAVsshould not harm other aircraft or the public. (Page 3: “While ensuring‘no harm’ to other NAS customers and public”)

The article Zone Ready for Drone, Apr. 7, 2006, on the web site for theFAA's Air Traffic Organization Employees states that,

-   -   Since March 29, a temporary flight restriction . . . has limited        access to the airspace along almost 350 miles of the border,        expanding an earlier TFR near Nogales. The restriction is in        effect nightly from 6 p.m. to 9 a.m., although that time can be        expanded by issuance of a Notice to Airmen. Aircraft wishing to        fly in the TFR when it is active must receive authorization from        air traffic control prior to entry. Once in, pilots are required        to maintain two-way communication with ATC and transmit a        discrete transponder code.

The reason for the TFR is to enable Predator UAVs to patrol the border.The article quotes Stephen Glowacki, a Systems Safety and Proceduresspecialist with the FAA's Air Traffic Organization as saying:

-   -   This is an extreme situation that has been presented to us,”        states Stephen Glowacki, a Systems Safety and Procedures        specialist with the FAA's Air Traffic Organization, stressing        the nation's security. “We have been working with U.S. Customs        and Border Protection to try and answer this situation.”    -   Inserting UASs into the National Airspace System is not a simple        feat. According to Glowacki, the technology and certification        that will permit unmanned aircraft to “see and avoid” other air        traffic is still eight to ten years away. In the mean time, a        carefully controlled environment is needed.

The track record of current UAV systems shows two major problem areas:

a. The communications link between the UAV and the ground station isunreliable, even at short ranges.

A recent example is the December 2006 crash of Lockheed Martin's PolecatUAV. When it lost communications with the ground it deliberately crasheditself to avoid flying into civil airspace. (See the article Lockheed'sPolecat UCAV Demonstrator Crashes in Aviation Week & Space Technology,Mar. 19, 2007, page 44.)b. Autonomous Mode is not always very smart.On Apr. 25, 2006 the Predator UAV being used by the U.S. Customs andBorder Protection agency to patrol the border crashed in Nogales, Ariz.According to the NTSB report (NTSB Identification CHI06MA121) when theremote pilot switched from one console to another the Predator wasinadvertently commanded to shut off its fuel supply and “With no enginepower, the UAV continued to descend below line-of-site communicationsand further attempts to re-establish contact with the UAV were notsuccessful.” In other words, the Predator crashed because the system didnot warn the remote pilot he had turned off the fuel supply and it wasnot smart enough to turn its fuel supply back on. (Note that this is thesame Predator discussed in the article Zone Ready for Drone previouslymentioned.)

SUMMARY OF THE INVENTION

It is important when flying a UAV in an airspace shared with otheraircraft, both civilian and military, that collisions during all phasesof flight (including taking off and landing) not happen. The currentmethod for accomplishing this is to place restrictions on all othertraffic in an air corridor representing the path of the intended flightof the UAV, thereby inconveniencing other traffic and disrupting theNational Airspace System.

Synthetic Vision

One objective of the present invention is to allow UAVs to safely shareairspace with other users by using synthetic vision during at least someof the phases of the UAV's flight so that changes required to existingFAA rules and regulations are minimized.

This may be accomplished by requiring that during selected phases of theflight the UAV be flown by a remote pilot using a Synthetic VisionSystem such as the one taught by U.S. Pat. No. 5,904,724 Method andapparatus for remotely piloting an aircraft. These selected phasesinclude:

-   -   (a) When the UAV is within a selected range of an airport or        other designated location and is below a first specified        altitude. This first specified altitude may be set high enough        that, for all practical purposes, it may be considered        unlimited.    -   (b) When the UAV is outside the selected range of an airport or        other designated location and is below a second specified        altitude.

Each UAV flown under these conditions must be under the direct controlof a remote pilot whose sole responsibility is the safe operation ofthat UAV. The rules will be similar to those for operating pilotedaircraft with automatic pilot systems including those with autolandcapability.

UAVs not flying in airspace where the use of a Synthetic Vision Systemis required may be flown autonomously using an Autonomous Control System(ACS) as long as the following conditions are met:

-   -   (a) A remote pilot monitors the operation of the UAV at all        times.    -   (b) The ACS periodically transmits its identification, location,        altitude, and bearing. This information may also be broadcast by        UAVs when operated by remote pilots using Synthetic Vision.

All UAVs must use Radar (either active or passive) or other device todetect the range and altitude of nearby aircraft in order to perform“see and avoid” actions.

All UAVs must provide a means for Air Traffic Control (ATC) and thepilots of other aircraft to communicate directly with the remote pilot.

The preferred method for flying a UAV from one airport to another, suchas in ferrying UAVs, would be to have the remote pilot at theoriginating airport be responsible for taking off and flying the UAV tothe specified altitude. A remote pilot at the arrival airport would beresponsible for having the UAV descend and land. In between, once theUAV has reached the specified altitude and range the remote pilotmonitoring the flight can be at any convenient location.

Synthetic Vision may be enhanced by combining and/or overlaying it withthe video from one or more video or infrared cameras or from syntheticaperture radar.

The method described does not require material changes in the presentair control system. It would also make UAV flights safer than mostexisting piloted flights where “see and avoid” is accomplished bylooking out small windows providing a limited field of view and hopingyou see any nearby aircraft in time to avoid a collision.

Communication Link Failures

The exact cause of the failure of the communications link in the Polecatcrash mentioned previously has not been made public. Technical detailsfor UAVs are limited because the systems are developed by privateindustry which generally considers such information proprietary. Inaddition, these are mostly military programs which limits publicdisclosure even more. (Indeed, although the Polecat crash took place inDecember 2006, it was not publicly reported until March 2007.)

One factor that may cause a communication link to fail is if it is ahigh-bandwidth link since a high-bandwidth link is more susceptible tointerference from other signals than is a lower-bandwidth link. The useof a synthetic vision system allows a lower-bandwidth link to be usedwhich improves its reliability

Another factor that affects a digital communications link when digitalpackets are sent through a network (such as an Internet-style network)is that the latency of the data packets cannot be assured either becausethe path may change from packet to packet or because packets may belost. When data packets are lost the destination server usually timesout and a request to resend the packet is issued which further increasesthe latency. Packets may also be lost simply because the path to aserver takes longer than the server's timeout period, causing the serverto issue an unending series of requests to resend the packet. If apacket is lost, either outright or because the path is longer than thetimeout period, transmission of data may stop entirely as most peoplewho use the Internet have experienced.

Because each data packet may take a different path, data packets may bereceived out-of-order. Standard Internet browsers such as Firefox andMicrosoft Internet Explorer know to reassemble the packets in thecorrect order. A custom software application, such as that used tocontrol UAVs, must do likewise to avoid becoming confused as to what ishappening when.

Some communications link failures may simply be due to the failure ofthe system to measure and adapt to the changing latency of the datapackets. The importance of having the system measure and adapt tochanging latencies is discussed in U.S. Pat. No. 5,904,724 by thepresent inventor.

Minimizing Communications Link Failures

Communications Link Failures can be minimized by, first of all, properlydesigning the communications link to prevent the obvious types offailures described above.

The next step is to provide redundant communications links. In additionto the standard types of communications links, an emergency backupcommunications link can use the standard commercial cell phone networkas long as precautions are taken to keep hackers out. Casual hackers canbe kept out by using Caller ID so if the UAV receives a call from anunauthorized number it answers the line and immediately hangs up. Thereason this keeps out only casual hackers is because PBXs (PrivateBranch Exchanges) can be programmed to deliver any Caller ID number thePBX operator desires. Once the UAV User is authenticated the ACS hangsup and calls one or more preprogrammed telephone numbers to establish alink to be used for communications. Because of the time needed toestablish this link it may be desirable to keep the emergency backupcommunications link on hot standby during takeoffs and landings. Keepingthis link on hot standby during all phases of flight also provides abackup method for tracking the UAV by using the cell phone towertriangulation method. As with the standard communications links all datamust be securely encrypted and the User must be periodicallyauthenticated.

What to Do if the Communication Link Fails

If even the emergency backup Communications Link fails there is nochoice but to go to the Autonomous Control System (ACS). What ACS doesdepends on the flight profile of the UAV.

a. If the UAV is on the runway on takeoff roll and is below V1 (themaximum abort speed of the aircraft) the takeoff is aborted.

b. If the UAV is between V1 and V2 (the minimum takeoff safety speed forthe aircraft) the choice is nominally between aborting the takeoff (andoverrunning the runway) and taking off. If all other UAV systems areoperating properly, taking off is probably the better choice since itmay be possible to re-establish the communications link once the UAV isin the air. However, if the UAV is equipped with a tailhook and therunway is equipped with arresting cables a suitable distance before thephysical end of the runway, the UAV takeoff may still be safely aborted.The hook and arresting cable method is the standard method used onaircraft carriers for landing aircraft.c. If the UAV is above V2 the UAV takes off and uses the takeoff profilethat is assigned to each particular airport. It then climbs to analtitude high enough to avoid other traffic and, unless thecommunication link can be firmly established, flies to the nearestairport designated to receive UAVs in distress. Only in extreme casesshould the ACS fly the UAV to a designated crash site.

Autonomous Mode is not Always Very Smart or Even Bug-Free

As noted in the case of the Predator previously mentioned, it crashedbecause the system did not warn the remote pilot he had turned off thefuel supply and it was not smart enough to turn its fuel supply back on.This may have been a design oversight or it may have been a softwarebug. Complex computer programs always have bugs no matter how brilliantor motivated the programmer(s). Treating every software error as amistake to be punished only leads to paralysis so that no code getswritten. After a good faith effort is made to “get it right” the systemsmust be thoroughly tested. And they must be tested on the ground.

Testing

Complex systems are difficult to test, especially when one of its partsis a flying machine which, itself, is made up of several systems.Simulation of the individual subsystems is not good enough. A simulationof the entire system is also not good enough because, despite the bestefforts, a simulation might not completely characterize the actualhardware and how the different hardware systems act together. The answeris to use Hardware-in-the-Loop simulation where the actual hardware isused with simulated inputs. A good description of Hardware-in-the-Loopsimulation can be found in the article Hardware-in-the-Loop Simulationby Martin Gomez in Embedded Systems Design (Nov. 30, 2001). The exampleMr. Gomez used was an autopilot.

The Ground Station is already on the ground so the proper place to startis with an actual ground station. The simplest configuration is to usean actual ground station with a simulation port connected directly to acomputer that simulates the UAV. (See FIG. 3). That probably isn't goodenough because it only really tests the ground station. The next step isto use a ground station with an actual communication link. (See FIG. 4.)This tests the ground station and the communications link.

Since the idea is to test the UAV without actually flying it, the ideaof Hardware-in-the-Loop testing is to use as much of the UAVs hardwareas possible by using a computer to read the system's output controlsignals and present the proper sensor input signals. In between is asimulation of the physical model of how the UAV interacts with thephysical universe. The UAV lives in an analog universe where space andtime are continuously variable, subject only to the Planck Distance andPlanck Time. (The Planck length is the scale at which classical ideasabout gravity and space-time cease to be valid, and quantum effectsdominate. This is the ‘quantum of length’, the smallest measurement oflength with any meaning, roughly equal to 1.6×10⁻³⁵ m. The Planck timeis the time it would take a photon traveling at the speed of light tocross a distance equal to the Planck length. This is the ‘quantum oftime’, the smallest measurement of time that has any meaning, and isequal to 10⁻⁴³ seconds.) The UAV's universe is also massively parallel,which is why simulating it with a single computer which is forced toperform different functions sequentially may not always produce accurateresults. This can be ameliorated somewhat by oversampling and runningthe model faster than that required by Nyquist. (The Nyquist rate is theminimum; you don't have to settle for the minimum.)

Ideally each sensor input and each actuator output should have its ownprocessor and all the processors should be linked to a computer thatcontains the overall physical model of the UAV's universe (the UniverseProcessor). For example, the Universe Processor knows the location ofthe UAV, its attitude, its bearing, the air temperature and pressure,local weather, terrain, etc. This assumes that the sensors and actuatorsare completely characterized. If they are not, then the physical sensorsand actuators can be used with devices that provide the proper physicalstimulation to the sensors and measure the actual physical results ofthe actuators. The desired end result is that each device in the UAVflight hardware, especially if it contains software such as the FlightControl Computer, can be operated with its actual hardware and software.When the hardware or software is changed, the old device can beunplugged and the new version installed. This avoids the problem ofrelying on software that has been ported to hardware other than thehardware it runs on in the flight UAV. For example, the “C” programminglanguage can be difficult to port to different computers because thedefinition of a “byte” in “C” can be different depending on thecomputer. Also note that the speed of the link connecting thesensors/actuators to the Universe Processor is determined by the speedof the fastest sensor/actuator, which also sets the minimum update rateof the Universe Processor.

The type of operating system(s) used in simulation and testing isimportant. In particular, with a non-deterministic Operating System(such as Windows) you cannot count on getting the same result every timebecause the operating system includes random timing components. From thearticle “Basic concepts of real-time operating systems” by DavidKalinsky (Nov. 18, 2003):

-   -   The key difference between general-computing operating systems        and real-time operating systems is the need for “deterministic”        timing behavior in the real-time operating systems. Formally,        “deterministic” timing means that operating system services        consume only known and expected amounts of time. In theory,        these service times could be expressed as mathematical formulas.        These formulas must be strictly algebraic and not include any        random timing components. Random elements in service times could        cause random delays in application software and could then make        the application randomly miss real-time deadlines—a scenario        clearly unacceptable for a real-time embedded system.    -   General-computing non-real-time operating systems are often        quite non-deterministic. Their services can inject random delays        into application software and thus cause slow responsiveness of        an application at unexpected times. If you ask the developer of        a non-real-time operating system for the algebraic formula        describing the timing behavior of one of its services (such as        sending a message from task to task), you will invariably not        get an algebraic formula. Instead the developer of the        non-real-time operating system (such as Windows, Unix or Linux)        will just give you a puzzled look. Deterministic timing behavior        was simply not a design goal for these general-computing        operating systems.        This means you may not be able to duplicate a failure. If you        cannot duplicate a failure you cannot fix it. And, needless to        say, the use of a non-deterministic Operating System in any part        of the UAV flight hardware will result in a system that can        never be completely trusted.

Failure to do proper ground-based simulation can lead to expensiveand/or embarrassing incidents such as this one reported by Aviation Week& Space Technology (Feb. 26, 2007, page 18):

-   -   The F-22 continues to encounter bumps in its first air        expeditionary force deployment to Okinawa. The 12 aircraft from        Langley AFB, Va., spent an unscheduled week at Hickam AFB, Hi.,        after the leading four had to abort the trip's last leg. As the        Raptors reached the International Date Line, the navigation        computers locked up so the aircraft returned to Hickam until a        software patch was readied. “Apparently we had built an aircraft        for the Western Hemisphere only,” says a senior U.S. Air Force        official. When the F-22s arrived at Kadena AB, Okinawa, some        Japanese citizens held a protest against the aircraft's noise.        Although the F-22 is not a UAV the principle is the same.

Testbeds can be used for more than just verifying that the system worksas designed. They can also be used to verify that the system is designedproperly for the User.

In military programs, operational procedures can be developed andmilitary personnel can be ordered to follow them. And they will followthem to the best of their ability because their careers are on the line.That doesn't change the fact that people operating poorly designedsystems are more likely to make mistakes.

Producing UAVs for the commercial market requires a different mindset.Civilians cannot be ordered to use a system whose design makes mistakeslikely or maybe even inevitable. Civilians have the option to not buythe product if they don't like it. They also have the option to sue themanufacturer of a system whose design makes mistakes inevitable.Civilians injured on the ground also have the option to sue themanufacturer of a system whose design makes mistakes inevitable.

Perhaps the UAV Industry can learn from the Video Game Industry wherethe standard practice is to hold focus groups early in the game'sdevelopment using real video game players. Game Designers may not likethe players' comments about their game but the players represent thegame's ultimate customers. In addition, the video game companies employpeople whose sole job is to extensively play the game before it isreleased and take careful notes of bugs, which are then passed on to theGame Developers. Although it is tempting to cut short the time devotedto testing in order to get the product out the door, a game releasedwith too many bugs will be rejected by the marketplace and will fail.

UAV manufacturers making UAV systems for the Government are protectedfrom liability under the Supreme Court's 1988 decision in Boyle v.United Technologies Corp, 487 U.S. 500 (1988), where the Court held thatif a manufacturer made a product in compliance with the government'sdesign and production requirements, but it was defective and causedinjury, the victim could not sue the manufacturer.

Since UAV manufacturers making UAV systems for the civilian market donot have this protection they should consider who their customers reallyare. Although civilian UAV systems will probably be operated bycivilian-rated pilots (at least initially), in a sense the UAVmanufacturers are really designing their systems to meet therequirements of the Insurance Industry and doing proper on-groundtesting is essential in making UAVs that will fly safely in civilianairspace. Military UAVs should meet the same standard because the crashof a military UAV that injures or kills civilians could ignite apolitical firestorm that would ground the entire UAV fleet.

The Reasons for Using Synthetic Vision During at Least Takeoffs andLandings

There are several reasons why the use of synthetic vision during atleast takeoffs and landings can minimize the risk to the public.

a. The ACS must be programmed to deal with every possible problem inevery possible situation that might arise. This is probably not possibleuntil computers become sentient.

Even after 100 years of aviation, pilots still encounter situations andproblems that have not been seen before. The way they deal with newsituations and problems is to use their experience, judgment, and evenintuition. Pilots have been remarkably successful in saving passengersand crew under extremely difficult conditions such as when parts oftheir aircraft fall off (the top of the fuselage peels off) ormultiply-redundant critical controls fail (no rudder control). Computerscannot be programmed to display judgment. They can only be programmed todisplay judgment-like behavior under conditions that have already beenanticipated. UAVs should not be allowed to fly over people's housesuntil they are at least smart enough to turn on their own fuel supply.Even so, this assumes the computer program has no bugs.b. Complex computer programs always have bugs no matter how brilliant ormotivated the programmer(s). As an example, look at almost everycomputer program ever written.(See the article Embedded Experts: Fix Code Bugs Or Cost Lives by RickMerritt in EE Times, Apr. 10, 2006, as well as the article Entries fromthe Software Failure Hall of Shame, Part 1 by Tom Rhinelander in g2zero,Jul. 6, 2006. g2zero at www.g2zero.com is a community dedicated todiscussing and advocating ways to improve software quality.)While adding a sense-and-avoid capability to existing UAV systems isnecessary it will increase the code complexity and increase the numberof bugs in the software.c. An Unmanned Combat Aerial Vehicle (UCAV) will have little chanceagainst one flown by an experienced pilot using Synthetic Vision untilArtificial Intelligence produces a sentient, conscious Being. At thatpoint, all bets will be off because a superior sentient artificial Beingmay decide that war is stupid and refuse to participate. It may alsodecide that humans are obsolete or fit only to be its slaves.

Acceptable Risk

Since it is impossible to anticipate every possible problem that mightarise and it is impossible to write completely bug-free code it comesdown to what is an acceptable risk.

When a military aircraft is engaged in a military operation, a greatdeal of risk may be acceptable, especially if it is on a criticalmission.

It is unacceptable to expose civilian aircraft flying in civil airspace,as well as the public on the ground, to this same level of risk exceptunder truly exceptional circumstances.

Synthetic Vision puts a human directly in the loop and makes flying aUAV in civilian airspace at least as safe as flying an aircraft with thepilot onboard.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may best be understood by referring to the followingdescription and accompanying drawings which illustrate the invention. Inthe drawings:

FIG. 1 is a general illustration showing a circular area of Range 102around Airport 101.

FIG. 2 is a general illustration showing the airspace around Airport 101where UAVs must be flown by a remote pilot using synthetic vision. Thisairspace is represented by the hatched areas.

FIG. 3 shows the simplest system for simulating the UAV system where anactual ground station is connected directly to a simulation computerthat simulates the UAV.

FIG. 4 shows a system for simulating the UAV system that includes anactual communications link.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth toprovide a thorough understanding of the invention. However, it isunderstood that the invention may be practiced without these specificdetails. In other instances well-known circuits, structures, andtechniques have not been shown in detail in order not to obscure theinvention.

FIG. 1 shows a Distance Range 102 around Airport 101. While a circulararea is shown for convenience any area whose shape can be defined may beused such as a square, rectangle, or other polygon. While FIG. 1 showsthe area around an airport any other designated location may bespecified. FIG. 2 shows an altitude profile of the airspace surroundingAirport 101. When the UAV is within Distance Range 102 of Airport 101 atan altitude below Selected Altitude 201 the UAV must be flown by aremote pilot using a Synthetic Vision System such as the one taught byU.S. Pat. No. 5,904,724 Method and apparatus for remotely piloting anaircraft. When the UAV is outside Distance Range 102, within DistanceRange 203, and is below Selected Altitude 202 the UAV must also be flownby a remote pilot using a Synthetic Vision System. The airspace wherethe UAV must be flown by a remote pilot using a Synthetic Vision Systemis represented by the hatched areas in FIG. 2.

Each UAV flown under these conditions must be under the direct controlof a remote pilot whose sole responsibility is the safe operation ofthat UAV. The rules will be similar to those for operating pilotedaircraft with automatic pilot systems including those with autolandcapability.

UAVs flying beyond Distance Range 102, within Distance Range 203, andabove Altitude 202 may be flown autonomously using an Autonomous ControlSystem (ACS) as long as the following conditions are met:

-   -   (a) A remote pilot must monitor the operation of the UAV at all        times. A remote pilot may monitor several UAVs simultaneously        once it is established that this practice may be safely        performed by a single pilot. For example, it may be preferable        to have two remote pilots work as a team to monitor ten UAVS        than to have each remote pilot separately monitor a group of        five UAVs.    -   (b) The ACS must periodically transmit its identification,        location, altitude, and bearing. This may be done through the        use of a speech synthesis system on a standard aircraft        communications frequency. This is for the benefit of pilots        flying aircraft sharing the airspace. It may also be done        through an appropriate digital system such as the one taught in        U.S. Pat. No. 5,153,836 Universal dynamic navigation,        surveillance, emergency location, and collision avoidance system        and method adopted by the FAA as ADS-B. This information may        also be broadcast by UAVs when operated by remote pilots using        Synthetic Vision.

All UAVs must use radar (either active or passive) to detect the rangeand altitude of nearby aircraft in order to perform “see and avoid”actions. An example of a passive radar system is taught by U.S. Pat. No.5,187,485 Passive ranging through global positioning system. Otherdevices for detecting the range and altitude of nearby aircraft may alsobe used.

All UAVs must provide a means for Air Traffic Control (ATC) and thepilots of other aircraft to communicate directly with the remote pilot.This may be accomplished by having the communication link between theremote pilot and the UAV relay communications with a standard aircrafttransceiver onboard the UAV.

Distance Range 203 extends to where it meets the area covered by anotherdesignated location such as another airport. The entire area covered byDistance Range 203 is termed a Designated Area. Another type ofDesignated Area is a large body of open water where the minimum safealtitude is determined by the height of a large ship riding the crest ofa large wave.

The preferred method for flying a UAV from one airport to another, suchas in ferrying UAVs, would be to have the remote pilot at theoriginating airport be responsible for taking off and flying the UAV tothe specified altitude. A remote pilot at the arrival airport would beresponsible for having the UAV descend and land. This is similar to thelongstanding practice of using Harbor Pilots to direct the movement ofships into and out of ports. In between the originating airport anddestination airport, once the UAV has reached the specified altitude andrange the remote pilot monitoring the flight can be at any convenientlocation.

Long delays in the communications link (such as through geosynchronoussatellites) make flying the UAV by direct control using synthetic visionmore difficult and should be avoided.

The method described does not require material changes in the presentair control system. It would also make UAV flights safer than mostexisting piloted flights where “see and avoid” is accomplished bylooking out small windows providing a limited field of view and hopingyou see any nearby aircraft in time to avoid a collision.

While preferred embodiments of the present invention have been shown, itis to be expressly understood that modifications and changes may be madethereto.

What is claimed is:
 1. A system for safely flying an unmanned aerialvehicle in civilian airspace comprising: (a) a ground station equippedwith a synthetic vision system; (b) an unmanned aerial vehicle capableof supporting said synthetic vision system; (c) a remote pilot operatingsaid ground station; (d) a communications link between said unmannedaerial vehicle and said ground station; (e) a system onboard saidunmanned aerial vehicle for detecting the presence and position ofnearby aircraft and communicating this information to said remote pilot;whereas said remote pilot uses said synthetic vision system to controlsaid unmanned aerial vehicle during at least selected phases of theflight of said unmanned aerial vehicle, and during those phases of theflight of said unmanned aerial vehicle when said synthetic vision systemis not used to control said unmanned aerial vehicle said unmanned aerialvehicle is flown using an autonomous control system, wherein saidselected phases of the flight of said unmanned aerial vehicle comprise:(a) when said unmanned aerial vehicle is within a selected range of anairport or other designated location and is below a first specifiedaltitude; (b) when said unmanned aerial vehicle is outside said selectedrange of an airport or other designated location and is below a secondspecified altitude.
 2. The system of claim 1 further comprising a systemonboard said unmanned aerial vehicle for periodically transmitting theidentification, location, altitude, and bearing of said unmanned aerialvehicle.
 3. The system of claim 1 further comprising a system onboardsaid unmanned aerial vehicle for providing a communications channel forAir Traffic Control and the pilots of other aircraft to communicatedirectly with said remote pilot.
 4. A system for safely flying anunmanned aerial vehicle in civilian airspace comprising: (a) a groundstation equipped with a synthetic vision system; (b) an unmanned aerialvehicle capable of supporting said synthetic vision system; (c) a remotepilot operating said ground station; (d) a communications link betweensaid unmanned aerial vehicle and said ground station; (e) a systemonboard said unmanned aerial vehicle for detecting the presence andposition of nearby aircraft and communicating this information to saidremote pilot; whereas said remote pilot uses said synthetic visionsystem to control said unmanned aerial vehicle during at least selectedphases of the flight of said unmanned aerial vehicle, and during thosephases of the flight of said unmanned aerial vehicle when said syntheticvision system is not used to control said unmanned aerial vehicle saidunmanned aerial vehicle is flown using an autonomous control system, andwhereas the selected phases of the flight of said unmanned aerialvehicle comprise: (a) when said unmanned aerial vehicle is within aselected range of an airport or other designated location and is below afirst specified altitude; (b) when said unmanned aerial vehicle isoutside said selected range of an airport or other designated locationand is below a second specified altitude.
 5. The system of claim 4further comprising a system onboard said unmanned aerial vehicle forperiodically transmitting the identification, location, altitude, andbearing of said unmanned aerial vehicle.
 6. The system of claim 4further comprising a system onboard said unmanned aerial vehicle forproviding a communications channel for Air Traffic Control and thepilots of other aircraft to communicate directly with said remote pilot.7. A method for safely flying an unmanned aerial vehicle as part of aunmanned aerial system equipped with a synthetic vision system incivilian airspace comprising the steps of: (a) using a remote pilot tofly said unmanned aerial vehicle using synthetic vision during at leastselected phases of the flight of said unmanned aerial vehicle, andduring those phases of the flight of said unmanned aerial vehicle whensaid synthetic vision system is not used to control said unmanned aerialvehicle an autonomous control system is used to fly said unmanned aerialvehicle; (b) providing a system onboard said unmanned aerial vehicle fordetecting the presence and position of nearby aircraft and communicatingthis information to said remote pilot; wherein said selected phases ofthe flight of said unmanned aerial vehicle comprise: (a) when saidunmanned aerial vehicle is within a selected range of an airport orother designated location and is below a first specified altitude; (b)when said unmanned aerial vehicle is outside said selected range of anairport or other designated location and is below a second specifiedaltitude.
 8. The method of claim 7 further comprising the step ofproviding a system onboard said unmanned aerial vehicle for periodicallytransmitting the identification, location, altitude, and bearing of saidunmanned aerial vehicle.
 9. The method of claim 7 further comprising thestep of providing a system onboard said unmanned aerial vehicle forproviding a communications channel for Air Traffic Control and thepilots of other aircraft to communicate directly with said remote pilot.10. A method for safely flying an unmanned aerial vehicle as part of aunmanned aerial system equipped with a synthetic vision system incivilian airspace comprising the steps of: (a) using a remote pilot tofly said unmanned aerial vehicle using synthetic vision during at leastselected phases of the flight of said unmanned aerial vehicle, andduring those phases of the flight of said unmanned aerial vehicle whensaid synthetic vision system is not used to control said unmanned aerialvehicle an autonomous control system is used to fly said unmanned aerialvehicle; (b) providing a system onboard said unmanned aerial vehicle fordetecting the presence and position of nearby aircraft and communicatingthis information to said remote pilot; whereas said selected phases ofthe flight of said unmanned aerial vehicle comprise: (a) when saidunmanned aerial vehicle is within a selected range of an airport orother designated location and is below a first specified altitude; (b)when said unmanned aerial vehicle is outside said selected range of anairport or other designated location and is below a second specifiedaltitude.
 11. The method of claim 10 further comprising the step ofproviding a system onboard said unmanned aerial vehicle for periodicallytransmitting the identification, location, altitude, and bearing of saidunmanned aerial vehicle.
 12. The method of claim 10 further comprisingthe step of providing a system onboard said unmanned aerial vehicle forproviding a communications channel for Air Traffic Control and thepilots of other aircraft to communicate directly with said remote pilot.